Remove the deprecated `concat_idents!` macro

In [137653], the lang and libs-API teams did a joint FCP to deprecate
and eventually remove the long-unstable `concat_idents!` macro. The
deprecation is landing in 1.88, so do the removal here (target version
1.90).

This macro has been superseded by the more recent `${concat(...)}`
metavariable expression language feature, which avoids some of the
limitations of `concat_idents!`. The metavar expression is unstably
available under the [`macro_metavar_expr_concat`] feature.

History is mildly interesting here: `concat_idents!` goes back to 2011
when it was introduced with 513276e595f8 ("Add #concat_idents[] and
about the same:

    let asdf_fdsa = "<.<";
    assert(#concat_idents[asd,f_f,dsa] == "<.<");

    assert(#ident_to_str[use_mention_distinction]
           == "use_mention_distinction");

(That test existed from introduction until its removal here.)

Closes: https://www.github.com/rust-lang/rust/issues/29599

[137653]: https://www.github.com/rust-lang/rust/pull/137653
[`macro_metavar_expr_concat`]: https://www.github.com/rust-lang/rust/issues/124225

1 files changed, 0 insertions, 4 deletions

diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index d32e6f1558e..bbf609a1b07 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -116,10 +116,6 @@ builtin_macros_concat_bytes_oob = numeric literal is out of bounds
 builtin_macros_concat_bytestr = cannot concatenate a byte string literal
 builtin_macros_concat_c_str_lit = cannot concatenate a C string literal
 
-builtin_macros_concat_idents_ident_args = `concat_idents!()` requires ident args
-
-builtin_macros_concat_idents_missing_args = `concat_idents!()` takes 1 or more arguments
-builtin_macros_concat_idents_missing_comma = `concat_idents!()` expecting comma
 builtin_macros_concat_missing_literal = expected a literal
     .note = only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`